1. Field of the Invention
This application relates to a system and method for water recovery from waste water such as mature fine tailings (MFT) water in the oilsands industry. The recovered water can be used during the bitumen extraction process or for steam generation. The heat is used for thermally efficient heating of the process water for mixing with bitumen ore or for steam generation. The recovered water can be used for steam generation in a commercially—available, non-direct prior art steam generator, as in OTSG (Once Through Steam Generator) and Boiler type facilities or as a process water to generate the oilsands ore slurry.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The present invention minimizes the need for settling fine tailings basins and enables a sustainable tailing practice of “reclaiming as you go”. This means continually reclaiming the excavated oilsands areas and the tailing pond as the mine progresses to a new location. This invention can also minimize the use of natural gas as a heat source for the extraction of heavy oil. Petroleum coke, coal or any other low grade, sulfur-rich carbonic fuel can be used instead of natural gas as the heat source. The sulfur content of the low grade carbonic fuel can be reacted with Lime Stone or Lime Sludge slurry waste from lime softening processes (such as WLS (Warm Lime Softener), widely used for OTSG water treatment in EOR facilities like SAGD or CSS). The reaction generates calcium sulfite or calcium sulfate, possibly anhydrate, which is extracted with the other fuel combustion and heated tailing solids (also called dry tailings). The presence of the calcium sulfite or calcium sulfate, together with the combustion and tailing solids, can increase the stability of a land-fill in order to support traffic.
The invention also improves thermal efficiency while minimizing the amount of CO2 generated as compared to the prior-art facilities used in an oilsands mine to generate the hot process water for the bitumen extraction. This is achieved due to the direct contact heat exchange between the combustion gas or superheated steam and the process water.
The steam can be used for Enhanced Oil Recovery (EOR) facilities or for the separation of bitumen and solvents from sand and water in open mining oil sand facilities. The water recovery process includes generation and separation of solids in a ZLD (Zero Liquid Discharge) environment, where a dry solid waste or semi-dry slurry that can support traffic is generated for effective disposal. The heat is recovered and used to heat the processed water, or to pre-heat boiler feed water for steam generation.
The invention can also eliminate the use of tailing ponds. However, for this option, large quantities of course tailing solids (like sand) will have to be filtered and trucked to the mine site instead of hydro transport as the transportation method.
Tailing pond water is a by-product of the oil, water and sand separation process. These ponds are becoming an increasingly significant environmental problem as the scale of oil sand recovery increases. 1606 ducks died in 2008 after mistakenly landing in contaminated ponds in northern Alberta. The tailing pond problem is continually escalating, as seen in 1979 when there were tens of millions of cubic meters of fine fluid liquid tailings. Currently in the Fort McMurray area there are close to eight hundred million cubic meters of MFT that covers about 60 square kilometers and require long term containment. Some of the oldest tailing ponds are located (irresponsibly), in close proximity to the Athabasca River. Leakages or extensive rainfall in the area can cause these tailing ponds to overflow directly into the river, with devastating effects on the natural environment and on the settlements downriver. The mature tailing water contains suspended fine sediments (less than 40 microns). This sediment can include: clay, heavy metals, hydrocarbons like bitumen, diluent, PAHs (Polycyclic Aromatic Hydrocarbons, which occur in oil and are a byproducts of burning fuels) and Naphthenic Acids, (surfactants found in all heavy oil), sulphate and sodium salinity. The PAHs tend to settle out with the fine sediments.
In Situ oilsands projects also generate large quantities of disposal water and sludge from their softeners in their facility water treatment plant, steam generation facility and in the oil separation process.
Another basic characteristic of an oil sands project is the use of heat and steam. This is a common characteristic for both surface oil sands mining and In-situ oilsands plants.
In mining, the processed water is heated using steam. Steam is also used to remove NCG and to separate diluent from the sand and the water.
In-Situ EOR facilities use steam for injection underground in order to separate the oil from the sand and move it to the surface. Typical EOR In-Situ facilities use SAGD and CSS (Cyclic Steam Stimulation—“Huff and Puff”) technologies.
Most of the work done to resolve the oil sands tailing ponds problem, and especially that of mature fine tailing ponds, is separate from the existence of the oil sand mine and the energy-intensive extraction plant. Using this approach (of separating the cause from the problem) will allow companies to defer the solution to the future, at which time the oil facilities plants will stop operating or have re-located. Such an approach can defer the mature fine tailing reclamation costs to the future, allowing maximization of the Oil Companies present profits while leaving the MFT problem to future generations. It is expected that the ERCB (Energy Resources Conservation Board) will reinforce actions to resolve the MFT problem. In a recent presentation done by the ERCB, it was said that “Fluid tailing volumes are growing steadily . . . no fluid tailings pond reclaimed . . . and neither the public nor the government is prepared to continue to accept commitments that are not met and increasing liabilities”. The strategy currently in use by Alberta regulators is to force oil producers to implement at least a partial solution for the problems associated with oil sand tailing ponds.
A basic technical problem and/or disadvantage arises when delaying the resolution of the MFT problem to the future: where the oil is recovered, it would be uneconomic to use an intensive energy method, which uses extensive heat to resolve the fine tailings pond problem. In the present invention, the heat used to resolve the MFT problem is recovered to produce hot water and steam that is used by the oil sand production facility, with minimal energy waste. The overall thermal efficiency of the invention, (which will be reflected in the volume of CO2 emitted) for operation of an oilsands mine plant, is no significantly higher than using steam boilers, as is typically done today to generate steam that is used to heat the process water used for bitumen extraction. This is true even without considering the other advantages of the current invention compared to the prior-art steam generator; advantages like resolving the MFT problem, reduction of fresh water consumption and the use of low grade fuel (like petcoke) instead of natural gas. In the future, if the heat energy cannot be consumed by a producing oilsand facility, the heat energy will be wasted which will make the implementation of my invention to consume the MFT pond unfeasible. Other methods (like thickening, centrifuge, weather drying and water capping) that do not use intensive heat can still be used even when the oilsand mines are not in operation. The issue outlined above is one corporate present commercial disadvantage of the invention as compared to other solutions for the MFT.
However, there is no commercially feasible solution currently in use that completely resolves the oil sand tailing problem in Alberta. There are several activities being carried out by the oil sand producers that are at different R&D stages. The technologies considered which are being tested by the industry include: Evaporation Dry and Freeze Thaw, In-Situ Densification (coke capping), Thickened Tailing, Accelerated Dewatering, Centrifuge MFT, MFT Water Capped Lake and Consolidated Tailing (CT).
Currently, there is a large-scale centrifuge pilot project in the works. The tailing ponds require either mechanical or chemical manipulation before subjecting the tailing fine clays to the spin dry cycle. To consolidate its tailings (CT), gypsum, a byproduct of the flue gas system for scrubbing out sulphur, is added, possibly with lime. The theory is that the gypsum interacts electrostatically with the clay and the weight of the added sand squeezes out the water. The thickening process, however, uses flocculants. The flocculants are organic polymers that increase the amount of settling in order to generate non-segregating tailings. The chemical treatment, in which very long molecules stick to different clays and interact mechanically, is enhanced through the addition of sand.
Another activity uses CO2. High purity CO2 is the by-product of a hydrogen plant. The CO2 causes a very slight acidification which helps release calcium ions. Most importantly, it also has an electrostatic effect and reacts chemically with the sediment. Whatever the process, the resulting dry stackable tailings have similar properties. The only commercially operated options are the CT and the MFT Water Capped Lake. Field pilots are currently being done for the Centrifuge MFT, the Accelerated Dewatering and thickened tailings. Most of the methods used by the industry include natural (or accelerated) dewatering. Relying on dry weather in Fort McMurray can be tricky. Project execution personnel are well aware of the challenges involved in reducing the moisture content of the soil (to increase soil compaction) due to unexpected precipitation in that area. There is also a chance that the precipitation in the area will increase in the future due to global warming. It is to be expected that drying the MFT will become even more challenging. The prior-art commercially available thickening tailing process and the MFT centrifuge or thickening process can be incorporated into the invention to increase the total amount of treated tailing and solids (dry tailings) removed. The thickened tailing, from flocculants enhanced thickening process or from a centrifuge process, can be used in my invention to produce solid waste, which can be used as back-fill for supporting traffic, thus increasing the amount of MFT consumed.
The present invention is based on the opportunity of solving the waste sludge or fine tailing water problem through the use of intensive heat processes, while recovering the water and heat. It can then be used for steam generation or for heating the process water in an oilsands extraction mine facility. Through this integrated approach, the tailing pond waste can be treated using energy-intensive processes (like DCSG—Direct Contact Steam Generation), to generate steam and solid wastes that can be disposed of in landfills or as back-fill mine construction material, mine refill, or direct reclamation in the oilsands ore excavation with minimal environmental impacts.
The definition of “Direct Contact Steam Generation” (DCSG) is that the heat is transferred between the liquid water and the combustion gas. This is accomplished through the direct mixing of the two flows (the water and the combustion gases). In the DCSG, the combustion pressure is similar to the produced steam pressure and the combustion gases are mixed with the steam. The combustion gas is mixture of CO2 steam, and possibly nitrogen and other gases. If steam is available, it can be used instead of the combustion gas mixture. The DCSG can also be named “Dryer” as it dries liquid wet tailings stream with combustion heat to produce a dried tailings stream and recoverable vapor.
In a Non-Direct Steam Generator (like a steam boiler with a steam drum and a mud drum) or a “Once Through Steam Generator” (OTSG), the heat transfer and combustion gases are not mixed and the heat transfer is done through a wall (typically a metal wall), where the pressure of the generated steam is higher than the pressure of the combustion. This allows for the use of an atmospheric combustion pressure. The product is pure steam (or a steam and water mixture, as in the case of the OTSG) without combustion gases.
Various patents have been issued, that are relevant to this invention. For example, U.S. Pat. No. 8,137,566, issued on Mar. 20, 2012 to Bozak et al., describes a method for treating tailing wastes. The method includes the use of jet pumps for agitating the liquid tailings for separation during the carbon phase. The tailings are flocculated and dewatered.
U.S. Pat. No. 4,969,520 Issued on Nov. 13, 1990 to Jan et al., describes a method for treating water for the production of steam for EOR while generating sludge (which is composed mainly of calcium carbonate and magnesium hydroxide). It also describes the separation and recovery of liquids from the sludge using centrifuge, and possibly using a flocculant. The solids are disposed of in a land fill.
U.S. Pat. No. 6,036,748 Issued on Mar. 14, 2000 to Wallace et al., describes a process for reducing the temperature for dissolving gases in black water, which is generated by a gasifier. The process includes flashing the water under low pressure to release the gas and generate evaporation within the black water. This reduces the water temperature while generating water vapor. Some of the water vapor is later condensed and recycled. The remaining, cooled black water is treated to remove the solids.
U.S. Pat. No. 6,706,199 issued on Mar. 16, 2004 to Winter et al., describes a method and apparatus for withdrawing and dewatering slag from a gasification system, using a sloped conveying lock hopper with rotating auger located in the conveyer of the lockhopper. The solid slag converges upwards while being separated from the water. U.S. Pat. No. 6,027,056 Issued on Feb. 22, 2000 to Maciejewski et al., describes a method for the assembly and slurrying of oil sand containing oversized lumps and water, while removing the oversized lumps and producing slurry suitable for piping to a separation facility.
Canadian patent 1,211,063 Issued on Sep. 9, 1986 to de Calonne, describes a method to treat tailing sludge, as generated in an open oilsands mine. The sludge is mixed with secondary fuel, like petcoke or coal. The water content of the mixture is then reduced to produce a mixture suitable for self-sustaining combustion. The combustion heat is used to produce steam (through a boiler heat exchanger) for use in the extraction process. The combustion process is done in a fluidized bed combustion furnace.
It is a goal of the present invention to provide a system and method for the use of waste water and any type of fuel while recovering the water and producing solid waste, to improve deep tar extraction EOR facilities, like SAGD or CSS.
It is another objective of the present invention to provide a system and method for the use of discharged water and tailing water, while recovering the water and removing solid waste, to improve oil sand extraction facilities like oil sand surface mining and excavating.
These and other objectives and advantages of the present invention will become apparent from a reading of the attached specifications and appended claims.